The disclosure generally relates to a power converter and, more particularly, to a control circuit applicable to various power converters with different input voltages.
In general, the conduction loss and the switching loss of a power converter are inversely proportional to each other. The best switching frequency of a power switch in the power converter is a switching frequency that minimizes the sum of the conduction loss and the switching loss, which is also the switching frequency that renders the power converter to reach the optimal power conversion efficiency.
The best switching frequency of the power switch varies with several external conditions, such as the input voltage, the output voltage, and the load. For example, the best switching frequency of the power switch in an application where the input voltage is 155V is different from the best switching frequency of the power switch in another application where the input voltage is 230V. Accordingly, the designer of a conventional control circuit is required to adjust the component parameters of the conventional control circuit in advance based on the magnitude of the input voltage of a particular power converter, so that the conventional control circuit is enabled to configure the power switch in the particular to operate at the best switching frequency.
However, the conventional control circuit is unable to dynamically adjust the best switching frequency of the power switch based on the change of the external conditions. Therefore, once the conventional control circuit is employed in other application with different input voltage, the conventional control circuit is unable to configure the power switch to operate at the best switching frequency under the application. As a result, the power conversion efficiency of the power converter would be greatly reduced.
In other words, the structure of the conventional control circuit is only applicable to particular power converters having the same input voltage, and not suitable to other power converter with different input voltage. Apparently, the application scope and application flexibility of the conventional control circuit are very restricted.